Variation in coumarin accumulation by stem age in Dendrobium thyrsiflorum (Orchidaceae) at different developmental stages

In this study, laser scanning confocal microscopy was applied to determine the localization and relative quantity of coumarins in stems of Dendrobium thyrsiflorum Rchb. f. (Orchidaceae) when plants enteredprofuse flowering and initial fruit period during reproductive growth stage. Stems at the two growth stages were collected respectively. Distribution of coumarins in the top, middle and basal parts of eachstem sample of 1, 2 and 3-year-old were observed by laser scanning confocal microscope. ANOVA and Tukey’s test were employed in the statistical analyses. The results showed that coumarins was locatedmainly in vascular bundle and its outer fiber cell wall, ground tissue cell wall and nearby, wall of epidermal cell and hypodermis cell as well. Statistical analyses indicated the significant or great significant difference presented in every part of stem of different ages in different growth periods except in the middle part during profuse flowering time. The content of coumarins reached its highest level when flowers profuse whereas at initial fruit stage that of coumarins was the lowest. Harvest activities of D. thyrsiflorum should be carried out when plants entered profuse flowering period in order to obtain abundant courmarins